1. Field of the Invention
The present invention relates to a display technique which can composite and display movie and graphic data.
2. Description of the Related Art
Nowadays, the broadcasting scene is making a shift from analog broadcasting to digital broadcasting to provide multi-channel broadcasts and high-definition contents. Display apparatuses which display such broadcast contents increasingly have larger screens and higher definitions.
Also, receivers are changing from those which merely display broadcast video images one-sidedly to those which include a mechanism that allows users to enjoy interactive services by data broadcasting and the like. As a result, the receivers are required to composite graphics data as in general personal computers.
As described above, along with the advent of digital broadcasting, and large-screen, high-definition display apparatuses, a display mode called “multi-window display” that simultaneously displays various media on a single display apparatus is expected. That is, a receiver is required to have a capability of smoothly compositing and displaying a plurality of movie data and graphics data.
However, in order to smoothly composite high-definition movie data and graphics data, high-speed memory transfer is required, resulting in an expensive system.
A technique for controlling a memory bandwidth used in a movie to reduce the cost of a system is disclosed in patent reference 1 (Japanese Patent Laid-Open No. 2003-298938). Patent reference 1 discloses a technique for decimating frames of streams with lower priority levels in accordance with the priority levels of streams upon displaying OSD (graphics) data during display of a plurality of streams.
Patent reference 2 (Japanese Patent Laid-Open No. 2007-057586) discloses the following technique. That is, when graphics and movie data are displayed on a display apparatus which can output images at a high resolution, graphics data whose resolution difference is easily recognizable for users are displayed at a high resolution, and movie data whose resolution difference is not easy to recognize even at a low resolution is rendered at a low resolution and is displayed in an enlarged scale.
The aforementioned related arts achieve a cost reduction of a system by suppressing the bandwidths used in movie data upon displaying graphics data.
However, movie data is displayed to have higher display quality than that of graphics data in some cases (for example, a case in which movies of a plurality of channels are concurrently recorded, a case in which graphics data of a channel indication, tone volume change indication, and the like have a smaller occupation ratio than movie data on the screen, and so forth). In such cases, the qualities of movie and graphics data have to be adaptively controlled, but the aforementioned related arts cannot solve these problems.
For example, the techniques disclosed in patent references 1 and 2 execute movie rendering control to reduce the memory bandwidth to be used, but they cannot execute graphics rendering control.
Also, these techniques cannot adaptively control a band used to render movie data and that used to render graphics data as the situation demands.